In modern private cars it is often desirable from design reasons to have as little space as possible between the hood of the vehicle and the components within the engine house, so that a low and advantageous profile can be attained. Moreover, it is desirable to make the engine house as small as possible, which implies that different components will be located closely to each other in the engine house. The consequence is that the hood has little ability to deform downwards when it is hit by a soft object, such as a hit pedestrian that is thrown up on the hood. The risk for serious injuries when a hit pedestrian strikes the hood can be devastating.
In the aim to reduce such a risk, it has been proposed that when a pedestrian is hit the hood is raised to provide for an increased deformation space. When a pedestrian is hit, the idea has been to quickly raise the rear portion of the hood, while the front portion remains locked to the body of the vehicle by means of a regular hood lock at the front of the hood. This is appropriate for speeds within low intervals of about 20-60 km/h, since the benefits of such a hood raising decreases at higher collision speeds.
An important aspect is the lifting devices that are intended to facilitate the quick raising of the rear portion of the hood, which is required to provide for the above mentioned deformation space. Future laws for the protection of pedestrians are expected to require that the rear edge of the hood can be raised in a few hundredths of a second, why the performance of the lifting device will be focused on.
Yet a desire for these lifting devices is that they can be made reversible, i.e. that the lifting device can be restored to its original position after its activation, e.g. when colliding with an other object than a pedestrian and the hood is raised in any case. Often, pyrotechnical solutions are used to activate the lifting device, but these are not reversible in that sense, but must be replaced by a new pyrotechnical unit in the case the lifting device has been activated. Moreover, they require reliable information regarding the accident so that unnecessary activations are avoided, which implies extensive detection and data processing equipment.
Instead, it has been proposed that electromagnets in the form of solenoids are used for activating the lifting device. These are reversible why the above mentioned detection and data processing equipment can be made less comprehensive. Additionally, the system is active as well as pedestrian friendly after each restoration, unlike pyrotechnical systems which require replacements at a garage to become functional again.